Silicone resins have been noted since their introduction for their ability to withstand high temperatures. This property has been utilized in alkyd and acrylic paints containing volatile organic solvents for many years. But the use of such paints is being restricted more and more by legislation in many states, led by California, which severely limits the amount of such solvents, particularly the photochemically reactive solvents, that may be used in paints.
There is a need, therefore, for a silicone-containing paint having a low content of volatile organic solvents that has a long shelf life, is easily applied by brush or spray, gives good coverage, and provides a coating after exposure to high temperatures that is smooth and continuous.
A storage stable aqueous aerosol coating composition is taught by Learner in U.S. Pat. No. 4,578,415. The sole binder in that composition is a water soluble ammonium salt of a drying oil-modified, low molecular weight acrylic copolymer.
Now, it has been discovered that a stable solution of a solid silicone and the acrylic copolymer of Learner can be made and that the silicone will survive the curing of a paint made from the solution and the burning of the acrylic component to provide a protective coating on a barbeque grill or the like at temperatures up to about 1300.degree. F. (about 700.degree. C.).
It is an object of this invention to provide an aqueous coating composition containing a solid silicone resin in solution that is stable at room temperature for as long as 18 months and for five months at 120.degree. F.
It is a further object of this invention to provide an aqueous coating composition comprising an acrylic resin binder that is burned off from the substrate at a high temperature and a silicone binder that provides an unbroken film on the substrate at still higher temperatures.